1. Field of the Invention
The present invention is related to a light emitting diode (LED) apparatus and a manufacturing method thereof, and more particularly to an alternating current driven (AC-driven) white LED apparatus manufacturing method, and an AC-driven white LED apparatus capable of achieving a high color rendering, a high light emitting efficiency and a stable chromaticity coordinate.
2. Description of the Related Arts
With reference to FIG. 1 for a schematic view of a LED array as disclosed in U.S. Pat. No. 6,957,899, the LED array 1 comprises an AC power supply 12, a first LED array 14 and a second LED array 18. In FIG. 1, the first LED array 14 and the second LED array 18 are composed of a plurality of micro-LED chips connected in series with each other and arranged on a same plane 10. An AC voltage with a positive half wave period is applied to drive the first LED array 14 to emit light, and an AC voltage with a negative half wave period is applied to drive the second LED array 18 to emit light, respectively. In general, the utility power of each different country has an AC frequency with 50˜60 Hz which is greater than the frequency required for the duration of vision of human beings, so that we cannot visually distinguish the alternating light emissions of the first and second LED arrays 14, 18 in the LED array 1, thereby achieving the objective of AC-driven applications.
At present, the yield rate of the GaN-based LED chips is unable to provide a uniform brightness or a 100% light emitting efficiency of each micro-LED chip. therefore if an AC voltage is applied to drive the first LED array 14 to emit light, as we know, light and heat will be generated. Therefore, the temperature and voltage will be deviated easily to cause a non-uniform light emission. Furthermore, if an additional AC voltage of the power supply 12 produces a pluse onto the light emitting device, the LED chip in the light emitting device may be broken easily, hence, the reliability will become a big issue as well as a major drawback of the disclosed LED array in this invention.
To overcome the aforementioned drawback of the GaN LED array disclosed in U.S. Pat. No. 6,957,899, a light emitting device as shown in FIG. 2 is disclosed in TW Pat. Publication No. 200826320, wherein the light emitting device comprises at least one correction circuit 20 to serve as a temperature and voltage compensation circuit provided for the operation of an AC-driven LED component 21 and achieve the effect of absorbing pluses. However, the aforementioned invention still has a drawback of failing to compensate the color rendering during light emitting.
With reference to FIG. 3 for a schematic view of a LED device disclosed in U.S. Application Publication No. 20090109151, wherein the white light emitting apparatus 30 is composed of two groups of the AC-driven LED 31 and 32, with different emission wavelengths from each other, and a phosphor material 33 to improve the color rendering. One of the methods is to provide an AC-driven blue-emitting LED and an AC-driven green-emitting LED, and a red-emitting phosphor is encapsulated on the AC-driven blue-emitting LED. Another method is to provide an AC-driven blue-emitting LED and an AC-driven red-emitting LED, and a phosphor is encapsulated on the AC-driven blue-emitting LED. The phosphor can absorb a part of the radiation emission from the blue-emitting LED and itself emit in spectral regions ranging from blue to red. Although, the prior art discloses the methods to improve the color rendering of white LED, yet the transfer efficiency of red-emitting phosphor, in the spectral region ranging from 600 to 630 nm, is not satisfactory even though the manufacturing technology is very mature. Hence, the first method can improve the color rendering, but it is hard to effectively enhance the light emitting efficiency of the light emitting apparatus. Moreover, the second method has the potential to improve the color rendering and avoid the decrease of light emitting efficiency. It is noteworthy that, if the group of the AC-driven red-emitting LED is made by the AlInGaP-based compound semiconductors, it will cause a worse stability in an operation ambiance of higher temperature due to the energy band gap of the AlInGaP is easy to shrink when the ambient temperature increases. In other words, it is hard to control the chromaticity coordinate of the white LED due to the large drift of the emission wavelength. Hence, the method still has the drawback in practical application.
With reference to FIG. 4 for a schematic view of a LED device disclosed in U.S. Publication No. 20080218098, a bridge rectifying circuit 40 composed of another set of LEDs is added to improve the reliability of operating an AC-driven LED device and protect a LED array 41. However, the bridge rectifying circuit 40 is directly formed on a substrate used by the LED array 41 and disposed at an external edge. In other words, the LED array 41 and the bridge rectifying circuit 40 are produced in a same fabrication process, and the bridge rectifying circuit 40 not only provides an AC-to-DC conversion function, but also has the function of emitting light. However, this method is unable to produce a high emitting efficiency LED assembly with different light emission wavelengths on the same substrate by the epitaxial and chip fabrication process, thus, the method still has the drawback of failing to provide the effect of compensating the color rendering.
In view of the aforementioned shortcomings of the prior arts, the inventors of the present invention based on years of experience in the related industry to conduct extensive researches and experiments, and finally developed a light emitting device according to the present invention to overcome the shortcomings of the prior arts.